Microelectronic devices, such as semiconductor devices and field emission displays, are generally fabricated on and/or in microelectronic workpieces using several different types of machines (“tools”). Many such processing machines have a single processing station that performs one or more procedures on the workpieces. Other processing machines have a plurality of processing stations that perform a series of different procedures on individual workpieces or batches of workpieces. In a typical fabrication process, one or more layers of conductive materials are formed on the workpieces during deposition stages. The workpieces are then typically subject to etching and/or polishing procedures (i.e., planarization) to remove a portion of the deposited conductive layers for forming electrically isolated contacts and/or conductive lines.
Plating tools that plate metals or other materials on the workpieces are becoming an increasingly useful type of processing machine. Electroplating and electroless plating techniques can be used to deposit nickel, copper, solder, permalloy, gold, silver, platinum and other metals onto workpieces for forming blanket layers or patterned layers. A typical metal plating process involves depositing a seed layer onto the surface of the workpiece using chemical vapor deposition (CVD), physical vapor deposition (PVD), electroless plating processes, or other suitable methods. After forming the seed layer, a blanket layer or patterned layer of metal is plated onto the workpiece by applying an appropriate electrical potential between the seed layer and an electrode in the presence of an electroprocessing solution. The workpiece is then cleaned, etched and/or annealed in subsequent procedures before transferring the workpiece to another processing machine.
FIG. 1 illustrates an embodiment of a single-wafer processing station 1 that includes a container 2 for receiving a flow of electroplating solution from a fluid inlet 3 at a lower portion of the container 2. The processing station 1 can include an anode 4, a plate-type diffuser 6 having a plurality of apertures 7, and a workpiece holder 9 for carrying a workpiece 5. The workpiece holder 9 can include a plurality of electrical contacts for providing electrical current to a seed layer on the surface of the workpiece 5. The seed layer acts as a cathode when it is biased with a negative potential relative to the anode 4. The electroplating fluid flows around the anode 4, through the apertures 7 in the diffuser 6, and against the plating surface of the workpiece 5. The electroplating solution is an electrolyte that conducts electrical current between the anode 4 and the cathodic seed layer on the surface of the workpiece 5. Therefore, ions in the electroplating solution plate onto the surface of the workpiece 5.
The plating machines used in fabricating microelectronic devices must meet many specific performance criteria. For example, many processes must be able to form small contacts in vias that are less than 0.5 μm wide, and are desirably less than 0.1 μm wide. The plated metal layers accordingly often need to fill vias or trenches that are on the order of 0.1 μm wide, and the layer of plated material should also be deposited to a desired, uniform thickness across the surface of the workpiece 5.
One concern of many processing stations is that it is expensive to fabricate certain types of electrodes that are mounted in the reaction vessels. For example, nickel-sulfur (Ni—S) electrodes are used to deposit nickel on microelectronic workpieces. Plating nickel is particularly difficult because anodization of the nickel electrodes produces an oxide layer that reduces or at least alters the performance of the nickel plating process. To overcome anodization, nickel can be plated using a chlorine bath or an Ni—S electrode because both chlorine and sulfur counteract the anodizing process to provide a more consistent electrode performance. Ni—S electrodes are preferred over chlorine baths because the plated layer has a tensile stress when chlorine is used, but is stress-free or compressive when an Ni—S electrode is used. The stress-free or compressive layers are typically preferred over tensile layers to enhance annealing processes, CMP processes, and other post-plating procedures that are performed on the wafer.
Ni—S electrodes, however, are expensive to manufacture in solid, shaped configurations. Bulk Ni—S material that comes in the form of pellets (e.g., spheres or button-shaped pieces) cannot be molded into the desired shape because the sulfur vaporizes before the nickel melts. The solid, shaped Ni—S electrodes are accordingly formed using electrochemical techniques in which the bulk Ni—S material is dissolved into a bath and then re-plated onto a mandrel in the desired shape of the solid electrode. Although the bulk Ni—S material only costs approximately $4–$6 per pound, a finished solid, shaped Ni—S electrode can cost approximately $400–$600 per pound because of the electroforming process.
Another concern of several types of existing processing stations is that it is difficult and expensive to service the electrodes. Referring to FIG. 1, the anode 4 may need to be repaired or replaced periodically to maintain the necessary level of performance for the processing station. In many cases, an operator must move a head assembly out of the way to access the electrode(s) in the reaction vessel. It is not only time consuming to reposition the head assembly, but it is also typically awkward to access the electrodes even after the head assembly has been moved. Therefore, it is often difficult to service the electrodes in the reaction vessels.